Electrodeposition of nanocrystalline Co-W coatings from citrate electrolytes under controlled hydrodynamic conditions part 3: The micro- and macrodistribution of the deposition rates, the structure, and the mechanical properties

Abstract

Using a Hull cell with a rotating cylindrical electrode (RCE), the effect of the hydrodynamic conditions on the deposition rate and its micro- and macrodistribution and the composition and microhardness of the cobalt-tungsten coatings deposited from a citrate electrolyte containing cobalt sulphate (0.2 mol/l) and sodium tungstate (0.2 mol/l) at pH = 6.7 and the solution temperature of 60°C in the Re numbers range of 0–3000 is examined. It is shown that the hydrodynamic deposition conditions have no effect whatsoever on the surface roughness, but they slightly influence the electrolyte’s throwing power. The correlation between the intensity of the hydrodynamic flows, the deposition rate (due to the current efficiency’s increase), and the composition of the coatings (along with their distribution over the surface) is established. It is shown that certain modes of the process at a high deposition rate make it possible to reach a high uniformity of the coating’s composition with a high tungsten content, which results in obtaining the maximum surface microhardness.